OCC DHY 150 Gypsum Materials

Created by rachel_dunn 

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Gypsum produces a...

positive replication
models, casts, dies

Properties of gypsum

Accuracy
Strength and resistance
Compatability with impression materials
Ease of use
biologically safe

Gypsum is...

naturally occur
Calcium Sulfate Dihydrate

Type II

Plaster

Type III

Stone

Type IV

Improved stone

Gypsum is produced by...

Calcination

Calicination

Heating gypsum and removing water

Physical differences in gypsum is due to...

Calcination process

Plaster

First dental stone
Least expensive and weakest
thin consistency

Stone

used for diagnostic models and working casts
yellow in color
alpha-hemihydrate

Improved Stone

Putty Like

Water/Powder Ratio

Amount and temperature effects

Mixing with water turns a heminhhydrate into a ________

dihydrate

Exothermic

Heat is liberated during the reaction

Stone W/P ratio

100g/ 28-30 mL

Working or initial setting time

Length of time from the start of the mix until it reaches a semi-hard stage
Time allowed for manipulation

Final Setting Time

The length of time from the beginning of the mix until the mass has become ridgid

Loss of gloss

end of working time
5-7 mins.

Loss of exothermic reaction

end of setting time
30-40 mins.

Increasing Setting Time

Addition of borax
Increase water
cold water
less mixing

Decreased Setting Time

Addition of KSO4
Decrease water
Warm water
more mixing

Gypsum should be stored in an.....

air tight container

Hygroscopic expansion

When gypsum come in contact with water during the setting time

Alginate effects on gypsum

If alginate remains in a gypsum cast it may eat away the model

Add ____ to _____

dry; wet

Techniques for pouring study models

Double pour
single pour with wax base
single pour with base former

Double pour

Pour the positive replication of the oral cavity
Pour a base of gypsum and bind the two together

When forming a gypsum cast and base the base should be______ to the counter

parallel

Maxillary cast is shaped to a ____

point

Mandibular cast is shaped in a _____

horseshoe

The base of each arch should be ____ of the arch height

1/3

Bases should be ___ of the total occluded height

1/2

Ideal occluded cast height

2 1/2-3 inches

Maxillary cast trimming

Parallel to the central grooves of posterior teeth
Canine eminence to midline

Mandibular cast trimming

Canine to canine

Label casts with

Your name, patient's name, and date

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